Installing a water butt is a good home DIY project that will save you money (if your water is metered) and will help the environment. Butt in this context is another word for barrel.
If you have a readily accessible downpipe (preferably UPVC) running from the roof gutter, you can quickly install a butt and collect rainwater. This can be used to water the garden. Even in a drought you can keep your plants green and healthy.
If like me, without guttering and a butt, the rain from your shed roof runs onto a wooden deck, then by diverting the water away you also prolong the life of your decking. This is another good reason to install a rainwater butt.
Buy a nice big butt, the bigger the better. Standard UK water butts hold around 200 litres. Your water butt should not sit directly on the ground. Make sure you raise it on bricks or slabs (or buy a stand) to raise it to a height where a watering can can be placed on the floor beneath the rain water butt tap. Whether you choose a bargain (£20 or so) black butt or an ornate affair is up to you. Some manufacturers now produce water butts that are designed to look like old teracotta chimneys, wooden barrels or even beehives.
Place the butt on the stand next to the down pipe an make the pipe 4 cm below the line. Cut the down pipe with a hacksaw and fit the rain diverter unit. Reattach the rest of the down pipe to the bottom of the diverter.
Drill a hole in the side of the butt (if required) to inset the connector pipe that leads from the diverter. Attach the two and water should start filling the butt the next time it rains. Then come the next hosepipe ban you will still be able to water your garden in an environmentally friendly manner.
Do remember to keep the lid on the water butt. It stops algae, mosquitoes, small mammals and other unwanted guests getting in to your water butt.
About six months after setting my water butt up, I noticed the downpipe was coming away from the connector, no matter how hard I wedged it in. The solution was a wrap or two of ptfe tape inside the join and since then (three years now) I have had no problems with the water butt setup. My only thought is that I want to save more water than my slimline butt will hold, so I will replace it with a large one and use the current butt to capture rainwater landing on the roof of our seperate log store.